Cellular material



July 25,1944 y c. l. HANEY Erm. l' 2,354,260

CELLULAR MATERIAL Filed April 26. 1941 BY MERVINI E. MAm-m..

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Ratented July FQ 2,354,250 l cnLLULsa MATERIAL Clifford I.-'\ Haney andE. Martin, Cumberland, Md., assignors to Celanese Corporation ofAmerica, a corporation of Delaware Application April 2 6, 1941, SeriallNo. 390,542'

8f Claims. (Cl. 18-48) This invention relates to cellular materials, andrelates more particularly to cellular materials having abasis of aderivative of cellulose.

An object of our invention is the preparation of cellular materialshaving a. basis of a derivative of cellulose.

Another object of our invention is the preparation of said cellularmaterials in'a rapid 'and economical manner and in any desiredpredetermined manner.

Other objects of our invention will appear from the lfollowing detaileddescription and tlie accompanying drawing.

In the drawing,

Fig. 1 is a front elevational view, partly in section, showing a moldingpress adapted to produce the cellular materials of.ourA invention in theform of cakes or blocks, and

Fig. 2 is a side elevational view, partly in section, of a screw feedextrusion device for extruding said cellular materials in a continuousform. Like reference numerals indicate like parts throughout theseveralviews of the drawing.

with extreme rapidity and the cellulose derivative is expanded to astrong, ilrm, cellular material of low density and even texture.

Various liquids and liquid mixtures having a solvent, softening orswelling action on the derivatives of cellulose in the vapor state (allof which are included in the term having at least a swelling action asused hereinafter in the claims),

may be used in the preparation of these cellular materials. Examples ofthe liquids or liquid mixtures which may be employed are acetone, ethylalcohol, ethyl alcoholv and benzol, water, chloroform, ethylenedichloride, acetone and` ethyl or methyl alcohol, ethylene dichlorideand ethyl or The preparation of cellular materials having a basis of avderivative of cellulose has been proposed and methods whereby thesematerials may be prepared have been suggested. In accordance with onemethod, a solution of a derivative of cellulose in a volatile solvent isprepared and inorganic salts of appreciable particle size are mixedtherewith. After the solution has been suitably shaped and then set byremoval of the solvent,

the soluble salts are extracted with water from lular structure is notsatisfactory for many purposes.

We have now discovered that low density, cellular materials having abasis of a derivative 4of cellulose may be prepared rapidly andeconomically by adding to said derivatives of cellulose when iniinely-divided form, a volatile liquid which has in the vapor lstate atleast a solvent, swelling or softening action thereon,subjecting thetreat- Y ed material to elevated temperature and pressure .ina closedchamber, and, then, after the cellulose derivative particles are atleast partially converted, quickly releasing thevpressure therefrom.'Ihe sudden release of the 'pressure while the treated material is at anelevated temperature allows the liquid absorbed therein to vaporizemethyl alcohol, methyl chloride and ethyl or methyl alcohol, butylalcohol, diacetone alcohol, and gasoline hydrocarbons, as well asmixtures of the organic liquids with various amounts of water. lWhileall these liquids are suitable, we

preferably use either acetone, ethyl alcohol, and mixtures of theseliquids with water or benzol.

The liquids may be applied to the finely divided cellulose derivativesin various ways. 'I'he desired quantity of liquid or liquid mixture maybe sprayed or sprinkled on to the cellulose deriv-l uid is uniformlydistributed throughout the mass.

. Alternatively, the cellulose derivative particles or terial.Preferably, however, we employ from 3% to 20 on the weight of thefibers.

conveniently, the rfinely divided ceuulose de-` rivative having theliquid dispersed therein may be subjected to heat and pressure `in anymolding device wherein the temperature may be suitably .controlled andwherein the pressure may be quickly released. Thus, a molding press maybe used and the-pressure may be applied to `the finely -dividedcellulose derivative material by placing said material in a suitablyshaped mold and applying pressure thereto by means of a piston orplunger shaped to conform to the mold. Upon a sudden release of thepressure, the rapid expansion and vaporization of the. liquid absorbedin the mass causes the cellulose derivative material to expand greatlyto a firm cellular air or other gas under pressure.

2 f asiatico.v

l In addition, pigments may be incorporated in structure which nils themold. ,By utilizing a suitably shaped mold, the expanded cellularmaterial may be obtained in any desired form or shape. Ii' desired, thecellulose derivative material under high pressure may be extrudedthrough suitably shaped orifices and in this way cellular sheets, tubes,rods, etc., may be obtained. When extruded-into suitably shaped-moldsother shapes may be obtained depending upon the particular shape of themold.

The/pressure may be applied to the mold by mechanical means, byhydraulic means or by The pressure to which the material may besubjected will vary depending upon the ilnal product desired and may,for example, be from 1,000 to 20,000 lbs. per sq. inch. Preferably,however, the cellulose derivative materials are subjected to pressuresof somewhat over 5,000 lbs. per sq. inch, i. e. about 6.000 lbs. per sq.inch and the pressure then suddenly released to normal atmosphericpressure.

'Ihe heating of the mold or pressure chamber may be accomplished in anyconvenient manner such, foi example, as'by steam or oil heating jacketssurrounding the mold or pressure charnber, by heating the pressurechamber with gas flames, or by using electrical resistance coils. 'Ihetemperature to which the finely divided material is heated will, ofcourse, depend upon the amount of pressure applied and the time duringwhich the material is maintained under said pressure. The temperatureshould bebelow the decomposition temperature of the particular cellulosederivative being molded and may generally Y be from 140 C. to 250 C.Particularly desirable results are obtained with cellulose acetate, for

example, by heating to about 200 C. 'I'he material maybe placed in a,cool mold or pressure chamber, then subjected to pressure therein andthe mold or pressure chamber may then be brought up to the desiredtemperature and maintained at that temperature-for period of timedesired. Il' desired, the heat/may be applied while the pressure isbelngput on. In this way,

objects of very low density may alsobe obtained. When high pressures andtemperatures are employed, the time during which the celluloseAderivative material is subjected to these conditions is relativelyshort. Maintaining the mold 1 or pressure chamber closed for from y to 5minutes may be ample, depending upon the size or thickness of the objectbeing fabricated. Genf,-

substances may alsobe employed. Where cellulose acetate is used, it mayhave an acetyl value of from 40 to 62.5% (determined as acetic acid).

yIn order. to increase the strength or to modify theappearance orproperties of the objects being molded or extruded, fibrous or otherilllersmay be incorporated therein. Examples of such fl- -brous illlersare fibers of cotton. flax, hemp, ramie, jute and natural silk, whileexamples of other-'filling materlalsare cork-sawdust wood shavings,clay, asbestos, etc., or mixtures of these.

75 communicating with a tapering passageway 24 the material or thematerial may be dyed to obtain color effects. The cellulose derivativesmay be treated with suitable plastlcizers before they are expanded. Anysuitable plasticiaer may be employed such as, for example, dimethylphthalate, diethyl phthalate, dibutyl tartrate, triphenyl phosphate,tricresyl phosphate, dibutyl phthalate and mono-ethyl-p-toluenesulfonamide. Y.

The products made in accordance with our invention may be put to a largevariety of uses. Dueto their low density, the materials are very usefulas heat insulating material in refrigerators and in pipe coverings, anddue to their porosity they may be used as a structural sound proofingmaterial. They may also be used for covering or insulating electricalequipment, or, when made into relatively thin discs or sheets. may beused for filtration purposes. When the pores are sealed up by treatingthe surface of the expanded material with a solvent', or by heating saidmaterial to cause the surfaces to coalesce,

the material resists penetration by water and the high proportion of airsealed therein lends an extreme buoyancy to the material thus making itsuitable for use in life belts and life rafts to replace other materialswhich lose their buoyancyafter long contact with water. Not only may thematerial be sealed as above, but it may also beA sealed by insertingthin sheets of unplasticized organic derivatives of cellulose above andbelow the charge before closing the mold and then allowing the materialto expand as described.

In the drawing there are shown devices whereby the cellular materials ofour invention may be prepared.

In` Fig. l there is shown a molding press, generally indicated byreference numeral Il, comprising a heated mold Ii set on asuitablesupport I2 and arecip'rocating, heated, pressure head I3, the latterbeing mounted on a piston Il which operates under hydraulic pressureexerted an chamber II. The length of the stroke of the pis;

ton il is variable and may'be adjusted as desired by changing theposition of the cross-head It, which carries said piston, along thevertical supports I1. The cross-head Il may be locked at the desiredlevel by suitable means (not shown). Pressure head i2 is heated by anelectrical resistance coil il, while mold il is heated by means ofhotoil circulated through a heating jacketvll surrounding the mold, the hotoil entering through an inlet 2li and discharging through an outlet 2i.Other suitable heating means may, of course, be employed.

In operation of the device shown in Fig. 1, the pressure head il isforced down by piston Il into the previously filled mold Ii, and thecombined action of heat and pressure serves partially to convert thecellulose derivative contained` therein. The hydraulic pressure is thensuddenly released which allows the pressure head -II to rise as thecellulose derivative material expands." The vertical movement of thepiston is limited by the position oi' cross-head Il and this limitationon the movement of the piston determines the ultimate thicknessmf thecellular cake or block which is formed. The cake may be discharged fromthemold by means of a foot lever Il.

In Fig. 2,A wherein an extrusion device is shown, saiddevice comprises ahopper Il, in which the cellulose derivative 4material may be chargedscrew Il is suitably driven as by a chain drive Il' and the rotation ofsaid screwcarries the. cellulose derivative material forward. Thepassageway is heated as by electrical resistance coils 26. "Ihe taper ofthe passageway causes the pressure to increase gradually as thecellulose derivative material moves forward andthe latter is finallyforced under very high pressure into a f' heated discharge nonle 21provided with a narrow opening Il. The nozzle II'is likewise heated tothe desired temperature by means'of electrical resistance coils 2l. Asthe cellulose derivative material is discharged, the sudden release ofpressure permits the material to expand suddenly tofform a cellular rodIl. Ihe latter is carried away on a moving belt 3l.

In order further to illustrate our invention, but without'being limitedthereto, the following examples are given:

Example I Cellulose acetate fibers having an acetyl value of 53.5-to 54%are thoroughly pulped and the dried fibers are then exposed to acetonevapors by suspending the material over acetone in 'a closed chamber for6 hours at 22 C. By this treatment the fibers absorb about of theirweight of acetone. Approximatelyl l5 parts by weightof the treatedmaterial is then placed in a molding press provided with circular moldafter the mold has been heated to 200 C. by means of electricalresistance coils. The m'old is then closed and a pressure of 6,000 lbs.per sq.

inch is applied to the cellulose acetate. After this pressure has beenmaintained for 10 minutes, the pressure is suddenly released andl thecellulose acetate expands to form a cellular white cake of smooth,external surfaceV and ilrm texture, having a density of 0.21. When thepressure is maintained on the material for minutes before it isreleased. a product having a i'lilnsity of 0.27 isobtallled.

Example II and'after being maintained at that temperature for 5 minutesthe pressure is suddenlyreleased and the cellulose acetate allowed toexpand. The resulting cellular cake is of firm texture and of pithyappearance, and has a density of 0.10.

Example III Cellulose acetate ilbers having an acetyl value of 54 to54.5% are pulped and dried and 10% by weight of a mixture of equal partsof acetone and water is sprayed on to the fibers. The moist fibers aretumbled for 1 hour until the liquid is evenly distributed throughout themass. After being permitted to stand in a closed container for aboutl 24hours, 15 parts by weight of the treated ilbers are placed in the hotmold of a molding press which liasbeen heated to 200 C. The press isclosed. and a pressure of 6,000 lbs. per sq. inch is applied to thecellulose acetate. 'This pressure is maintained for 5 minutes and themold assenso I 3 contamina s' :cnam ausm screw u. 'me

is then opened quickly and the cellulose acetate allowed to expand. Thecellular cellulose acetate is a firm mass having a smooth surface, andhas a density of 0.12. When the press is closed for 5 15 minutes beforethe pressure is released, a material having a density of 0.1 9 isobtained.

' Example IV Cellulose acetate having anI acetyl value of w 54.5% isground to pass a 40- mesh screen and 15% by weight of water is sprayedon to the parti.

cles. The moist particles are tumbled for 6 hours until the liquid isevenly distributed throughout the mass. 10 parts by weight of thetreated particles are placed in the hot moldof a molding press which hasbeen heated Ato 200 C. and a pressure of 6,000 lbs. per sq. inchisapplied to the mass. After this pressure has -been maintained for 5minutes, the pressureis .suddenly zo released and the cellulose acetateexpands to a cellular mass having a density of ,0.129.

Example Vv released. The cellulose acetate expands to a firm, cellularcake having a density of 0.12.

:is Example VI treated particles are placed rin the hot mold of amolding press which has been heated to 180 C. and a pressure of 6,000lbs. per sq. inch is applied to the mass. After this pressure has beenmaintained for 5 minutes, the pressure is suddenly released and thecellulose acetate expands to a firm cellular mass having a density of0.086.

Example VII Cellulose acetate having an acetyl value of 40% and inailnely divided form is treated with water and tumbled so that a uniformmixture containing 5% of water based on the weight of the material isobtained. About 10 partsby weight of this material is placed in the hotmold of a molding press heated to 160 C. and a pressure of 6,000 lbs.per sq. inch is applied to the mass. This pressure is maintained for 1minute and is then sud- 30 denly released. The cellulose acetate expandswhen the pressure is released and forms a firm,

cellular mass having a density of 0.28.

It is to be understood that -the foregoing detailed description ismerely given by way of illustration and that many variations may be madetherein` without departing from the spirit of our invention.

Having described our invention, what we desire' to secure by LettersPatent is:

l.- Method of making cellular articles of low density containingcellulose acetate, which coniprises forming a mixture of particles o fcellulose acetate containing 15% by weight of ethyl alcohol, subjectingsaid mixture tothe action of elevated temperature at which ethyl alcoholnormally exists in the vapor state anda pressure o! about 0,000 lbs. persquare inch and then quickl! releasing the pressure. 2. Method of makingcellular articles of lo density containing cellulose acetate. whichcomprises lforming a mixturebf particles oi cellulose acetate containing5% by weight of acetone, subicctinc temperature at which water normally.exists in the vapor state and a pressure of about 6,000 lbs. per squareinch and then quickly releasing the pressure.

4. Method of making cellular articles of lowv density containingthermoplastic derivatives of cellulose, which comprises forming amixture oi' particles of a thermoplastic derivative of cellulose and aliquid which, under the conditions of temperature and pressure employed,has at least a swelling action on the derivative oi' cellulo,

ysubjecting said mixture to the action of elevated temperature at whichsaid liquid normally exists in the vapor state and a pressure of atleast 1,000 pounds per square inch, the amount of liquid emplayed beingfrom l to 40% on the weight oi the cellulose derivative, and thenquickly releasing the pressure.

5. Method o: making anular mucus` of low density containing celluloseacetate, which comprises forming a mixture of particles oi celluloseacetate and a liquid which, under the conditions v of temperature andpressure employed, has at least a swelling action on the celluloseacetate,

subjecting said mixture to the action oi' elevated temperature at whichsaid liquid normally exists in the vapor state and a pressure of atleast 1,000 pounds per square inch. the amount of liquid employed beingfrom l to `ir0% on the weight or the cellulose acetate, and then quicklyreleasing the pressure.

's assenso 6. Method oi making cellular articles oi low densitycontaining thermoplastic derivatives oi' cellulose, which comprisesforming a mixture oi particles ot a thermoplastic derivative oicellulose and a liquid which, under the conditions of temperature andpressure employed, has. at least a swelling action on the derivative ofcellulose by exposing said cellulose derivative particles to the actionof vaporsy oi' said liquid so that said vapors are absorbed thereby,subjecting said mixture to the action of elevated temperature' at whichsaid liquid normally exists in the vapor state and a pressure oi atleast 1,000 pounds per square inch. the amount of liquid employed beingfrom l to 40% on the weight 'ot the cellulose derivative, andfthenquickly releasing the pressure. e

' 7. Method of making cellular articles of low density containingcellulose-acetatef-which comprises iorming a mixture oi' particles oi'cellulose acetateand a liquid which, under the conditions of temperatureand pressure employed, hn at least a swelling action on the celluloseacetate by exposing said cellulose acetate particles to the action ofvapors of said liquid vso that said vapors are absorbed thereby,subjecting said mixturefo Y the action of elevated temperature at whichsaid liquid normally exists in the vapor state and a pressure o! atleast 1,000 pounds per square inch. the amount ot liquid employed beingfrom 1 to'40% on the weight of lthe cellulose acetate, and then quicklyreleasing the pressure.

8. Method of making cellular articles of. low density containingcellulose acetate, which comprises forming a mixture of particles ofcellulose acetate and a liquid which, under the conditions oftemperature and pressure employed, has at least a swelling action on thecellulose acetate, subjecting said mixture to the action ci' elevatedtemperature at which said liquid normally exists in the vapor state anda pressure o! at least 1,000 pounds per square inch, the amount o!liquid employed being trom 1 to 40% on the weight oi the celluloseacetate, and then extruding the said material so that the pressurethereon is quickly released, whereby a cellular material is formed.

